Heat exchangers

ABSTRACT

A heat exchanger having vertically disposed downcomer tubes connected at the bottom to vertically disposed spaced riser heat transfer tube bundles, shrouding forming a first vertically extending independent channel and a second independent channel surrounding downcomer tubes so that a portion of the heating fluid can flow upwardly in the first channel and thence downwardly around said downcomer tubes in the second channel by natural circulation.

United States Patent 1191 Meshii 4] HEAT EXCHANGERS [75] Inventor:Toshio Meshii, Kobe, Japan [73] Assignee: Atomic PowerDevelopmentAssociates, Inc., Detroit, Mich.

221 Filed: Nov. 3; 1971 [21] App1.No.: 195,143

[52] [1.8. CI. 122/32, 165/145 [51] Int. Cl. .L F22b 1/06 [58] Field ofSearch 122/32, 34; 165/74,

[5 61 References Cited UNITED STATES PATENTS 3,245,464 4/1966 Amrnonetal...,.. 122/32 x 3,254,633 6/1966 Ammon et al. 122/32 July3,1973

3/1964 Boni. Jr. et al. 122/32 X 6/1965 Ammon.... l. 122/32 'x PrimaryExaminer-Kenneth W. Sprague Attorney-Joseph M. Fitzpatrick, Edwin T.Grimes et al. 1

[57] ABSTRACT V A heat exchanger having vertically disposed downcomertubes connected at the bottom to vertically disposed spaced riser heattransfer tube bundles, shroud ing forming a first vertically extendingindependent channel and a second independent channel surroundingdowncomer tubes so that a portion of the heating fluid can flow upwardlyin the first channel and thence downwardly around said downcomer tubesin the second channel by natural circulation.

3 Claims, 2 Drawing Figures HEAT EXCHANGERS This invention relates toimprovements in the performance of heat exchangers and it isparticularly adapted for heat exchangers employing vertically orienteddowncomer tubes and riser heat transfer tube bundles. The invention isparticularly adapted, among other possible applications, for use inassociation with a nuclear reactor, such as one cooled by liquid metal,sodium circulating in the reactor heats, another system containingsodium at a primary heat exchanger, and the sodium of the secondarysystem is used to heat water at a secondary heat exchanger for purposesof driving a prime mover such as a turbine. Heat exchangers of this typeare constructed so that water downcomer tubes are connected at the topto a water inlet and at the bottom to parallel riser heat transfer tubebundles. The top ends of the riser tubes are connected to a vaporoutlet. Vapor is generated by the downward flow of liquid metal such assodium, passing downwardly around the heat transfer tube bundles from anupper inlet to a lower outlet. Heretofore, difficulty was experienceddue to the fact that the liquid metal flowed downwardly around thedowncomer tube, which had a small diameter. The heat transferred boiledthe water before it reached the riser tubes, thereby generatingthermalhydraulic instabilities. To eliminate this, a shroud or bulk headwas added between the downcomer tube and the riser heat transfer tubebundles, so that the liquid metal passed around the riser tube bundles,only. As a result of this construction, the instabilities wereeffectively eliminated, but then the downcomer tubes did not receive anyheat but, in fact, were cooled by the water flowing therethrough. Thisconstruction created a number of problems. Large temperature differencesoccurred at the connection between the riser tube bundles and thedowncomer tubes, thereby causing high thermal stresses in the tubestructure in this area. Also, a hydraulically unstable situation existedwhich caused cyclic type flow disturbances. In addition, high cyclicfatigue occurred due to the large temperature differ ences and thehydraulic instability. In addition, it was virtually impossible toutilize leakage detectors to indicate leakage in the tubes due to theuncertain flow pattern in these regions. Moreover, there was apossibility of concentration of impurities in this area due to thestagnant conditions and low temperatures.

The present invention involves a novel combination of elements combinedin such a way as to afford a very efficient solution to the difficultiesencountered with the prior art, as will become apparent as thedescription proceeds.

In view of the foregoing, this invention contemplates the provision of anew and improved heat exchanger embodying a steam generator shell, aplurality of vertically disposed downcomer tubes mounted within theshell and having upper inlets for a first fluid. Riserheat transfer tubebundles are mounted in parallel, spaced relationship with respect to thedowncomer tubes, and the lower ends of the downcomer tubes are connectedto the lower ends of said tube bundles. The riser tube bundles have anupper outlet for. the first fluid. The shell has an upper inlet for asecond fluid which is connected in fluid flow relationship with theupper ends of the riser heat transfer tube bundles. The shell has alower outlet for the second fluid which is in fluid flow relationshipwith the lower ends of the riser heat transfer tube bundles. A firstcylindrically shaped adjusting shroud is mounted adjacent the downcomertubes and extends from the upper ends of these tubes to a locationadjacent the second fluid outlet. The first adjusting shroud forms afirst substantially vertically extending independent channel, and asecond cylindrically shaped shroud is mounted is spaced relationshipbetween the downcomer tubes and the riser tube bundles and extendssubstantially the length of the downcomer tubes. The first and secondshrouds coact to define a second substantially vertically extendingindependent channel surrounding the downcomer tubes so that a portion ofthe second fluid can flow upwardly in the first channel and thencedownwardly around the downcomer tubes in the second channel by means ofnatural circulation.

There has thus been outlined rather broadly the more important featuresof the invention in order that the detailed description thereof thatfollows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described more fullyhereinafter. Those skilled in the art will appreciate that the concepton which this disclosure is based may readily be utilized as the basisfor the designing of other structures for carrying out the severalpurposes of the invention. It is important, therefore, that thisdisclosure be regarded as including such equivalent constructions as donot depart from the spirit and scope of the invention.

Several embodiments of the invention have been chosen for purposes ofillustration and description, and are shown in the accompanyingdrawings, forming a part of the specification, wherein:

FIG. 1 is a vertical, medial, sectional view of a heat exchangerconstructed in accordance with the concept of this invention; and

FIG. 2 is a vertical, medial, sectional view of a heat exchanger showinganother embodiment of my invention.

In the embodiment of FIG. 1, there is shown a steam generator shell 10,containing water downcomer tubes 12 which are connected to water inlets14. The downcomer tubes 12 are connected at the bottom to parallel riserheat transfer tube bundles 16 having upper outlets 18. Accordingly,boiler feed water enters through the inlets l4 and passes downwardlythrough the downcomer tubes 12, as indicated by arrows 20, and thencearound, as indicated by the arrows 22, and up through the riser tubebundles 16, as indicated by arrows 24, and out as steam through theoutlets 18, as indicated by arrows 26.

Still referring to FIG. 1, liquid metal, such as sodium, enters throughan upper inlet 28 and flows downwardly through the riser heat transfertube bundles 16, as indicated by arrows 30 and out through a loweroutlet 32, provided for the purpose. A tube-shaped adjusting shroud 34is mounted medially of the downcomer tubes 12. This shroud extends fromadjacent the water inlet 14 of the downcomer tubes to adjacent thesodium outlet 32. A second cylindrically shaped shroud 36 is mounted inspaced relationship between the downcomer tubes 12 and the riser tubebundles 16. This second shroud extends substantially the length of thedowncomer tubes. The two shrouds are arranged to provide a suitablespace around the downcomer tubes 12.

While the greater portion of the liquid metal or sodium which flowsdownwardly through the riser tube bundles l6 and thence out through theoutlet 32, a smaller secondary portion of this sodium continuously flowsupwardly inside the shroud 34, as indicated by arrow 38 and, thence,outwardly and downwardly, as indicated by arrows 40 around the downcomertubes 12, and back out the bottom as indicated by arrows 42, to returnto the main body of sodium flow. This secondary flow is effected bymeans of natural circulation caused by the increase in the density ofthe sodium which is cooled at the periphery of the downcomer tubes 12.That is, the sodium is continuously cooled by the downcomer tubes in theregion surrounding same, thereby causing the natural circulation. Thisflow of sodium raises the temperature of the water in the downcomer tube12 so that the difference between the water in the lower portion of thedowncomer tube and in the lower portion of the riser tube bundle 16 issubstantially reduced in comparison with conventional structures.Therefore, thermal stress in this region, as well as plate-out of theimpurities, is substantially eliminated and, in addition, heat transferis effected in the downcomer tube, thereby adding to the efficiency ofthe system.

In the embodiment of my invention shown in FIG. 2, there is provided asteam generator shell 44 containing water downcomer tubes 46 which areconnected to water inlets 48. The downcomer tubes are connected at thebottom to parallel riser heat transfer tube bundles 50 having upperoutlets 52. In this embodiment the boiler feed water enters through theinlets 48 and passes downwardly through the downcomer tubes, asindicated by arrows 54, and thence flows around, as indicated by arrows56, and up through the riser tube bundles 50, as shown by arrows 58, andout through the outlet 52, as indicated by arrows 60.

Still referring to FIG. 2, liquid metal, such as sodium, enters throughan upper inlet 62 and flows downwardly through the riser heat transfertube bundles 50, as indicated by arrows 64, and out through the loweroutlet 66. A tube-shaped adjusting shroud 68 is mounted outwardly of,and surrounding the downcomer tubes 46. It extends from the upper endsof the downcomer tubes down to a location adjacent the sodium outlet 66.This shroud is mounted in spaced relationship with respect to thegenerator shell and in spaced relationship with respect to the downcomertubes 46. A second cylindrically shaped shroud 70 is mounted in spacedrelationship between the downcomer tubes 46 and the riser tube bundles50, and extends substantially the length of the downcomer tubes. The twoshrouds are arranged to provide suitable space around the downcomertubes 46.

While the greater portion of the sodium which flows downwardly throughthe riser tube bundles 50 and thence out through the outlet 66, asmaller secondary portion thereof continuously flows upwardly in thecylindrical space between the shell and the first shroud 68, asindicated by arrows 72 and, thence, inwardly and downwardly, asindicated by arrows 74, around the downcomer tubes 46, and back out thebottom as indicated by arrows 76, to return to the main body of sodiumflow. This secondary flow is by means of natural circulation caused bythe increase in the density of the sodium which is cooled at theperiphery of the downcomer tubes 46. In the same manner as pointed outin connection with the description of the embodiment of FIG. 1, thisalso raises the temperature of the water in the downcomer tube so thatthe temperature difference between the water in the lower portion of thedowncomer tube and in the lower portion of the riser tube bundles S0 issubstantially reduced in comparison with conventional structures.

It will thus be seen that the present invention does indeed provide animproved heat transfer apparatus which is superior because of thereduction of temperature differentials, hydraulic instability, reductionof thermal stresses, reduction of cyclic fatigue, which has an increasedheat transfer area, and which reduces the possibility of concentrationof impurities, as compared to prior art such devices.

Although certain particular embodiments of the invention are hereindisclosed for purposes of explanation, various modifications thereof,after study of this specification, will be apparent to those skilled inthe art to which the invention pertains.

What is claimed and desired to be secured by Letters Patent is:

l. A heat exchanger comprising a steam generator shell, a plurality ofsubstantially vertically disposed downcomer tubes mounted within saidshell and having upper inlets for a first fluid, riser heat transfertube bundles mounted in parallel spaced relationship with respect tosaid downcomer tubes, the lower ends of said downcomer tubes beingconnected to the lower ends of said tube bundles, said riser tubebundles having an upper outlet for said first fluid, said shell havingan upper inlet for a second fluid and being in fluid flow relationshipwith the upper ends of said riser heat transfer tube bundles, said shellhaving a lower outlet for said second fluid, said lower outlet being influid flow relationship with the lower ends of said riser heat transfertube bundles, a first cylindrically shaped adjusting shroud mountedadjacent said downcomer tubes and extending from the upper ends of thedowncomer tubes to a location adjacent the second fluid outlet, saidfirst adjusting shroud defining a first substantially verticallyextending independent channel, a second cylindrically shaped shroudmounted in spaced relationship between the downcomer tubes and the risertube bundles and extending substantially the length of the downcomertubes, said first and second shrouds defining a second substantiallyvertically extending independent channel surrounding said downcomertubes, means interconnecting the upper ends of said channels in fluidflow communication, whereby a portion of the second fluid can flowupwardly in the first channel and thence downwardly around saiddowncomer tubes in the second channel by means of natural circulation.

2. A heat exchanger according to claim 1 wherein said downcomer tubesare disposed inwardly of said riser heat transfer tube bundles and saidfirst adjusting shroud is disposed inwardly of said downcomer tubes.

3. A heat exchanger according to claim 1 wherein said downcomer tubesare disposed outwardly of said riser heat transfer tube bundles and saidfirst adjusting shroud is disposed between said downcomer tubes and saidshell.

1. A heat exchanger comprising a steam generator shell, a plurality ofsubstantially vertically disposed downcomer tubes mounted within saidshell and having upper inlets for a first fluid, riser heat transfertube bundles mounted in parallel spaced relationship with respect tosaid downcomer tubes, the lower ends of said downcomer tubes beingconnected to the lower ends of said tube bundles, said riser tubebundles having an upper outlet for said first fluid, said shell havingan upper inlet for a second fluid and being in fluid flow relationshipwith the upper ends of said riser heat transfer tube bundles, said shellhaving a lower outlet for said second fluid, said lower outlet being influid flow relationship with the lower ends of said riser heat transfertube bundles, a first cylindrically shaped adjusting shroud mountedadjacent said downcomer tubes and extending from the upper ends of thedowncomer tubes to a location adjacent the second fluid outlet, saidfirst adjusting shroud defining a first substantially verticallyextending independent channel, a second cylindrically shaped shroudmounted in spaced relationship between the downcomer tubes and the risertube bundles and extending substantially the length of the downcomertubes, said first and second shrouds defining a second substantiallyvertically extending independent channel surrounding said downcomertubes, means interconnecting the upper ends of said channels in fluidflow communication, whereby a portion of the second fluid can flowupwardly in the first channel and thence downwardly around saiddowncomer tubes in the second channel by means of natural circulation.2. A heat exchanger according to claim 1 wherein said downcomer tubesare disposed inwardly of said riser heat transfer tube bundles and saidfirst adjusting shroud is disposed inwardly of said downcomer tubes. 3.A heat exchanger according to claim 1 wherein said downcomer tubes aredisposed outwardly of said riser heat transfer tube bundles and saidfirst adjusting shroud is disposed between said downcomer tubes and saidshell.